Minimally Invasive Glaucoma Surgery

Background: Approximately 1.4 % of the German population aged 35 to 74 suffers from glaucoma, which is one of the more common causes of blindness. The only evidence-based treatment option at present is lowering the intraocular pressure. Modern minimally invasive surgical procedures hold out the prospect of lowering the intraocular pressure without the risk of serious complications.

Methods: This is a selective review of pertinent publications retrieved by a search in PubMed, including randomized, controlled trials and meta-analyses.

Results: The intraocular pressure can be lowered with eyedrops, laser procedures, and surgery. Trabeculectomy is the reference standard in glaucoma surgery but leads to complications in 3–15% of cases. In minimally invasive glaucoma surgery, very small stents can be implanted to lower the intraocular pressure. These procedures have a better safety profile but are only indicated for mild or moderate glaucoma. The Kahook Dual Blade, iStent inject, and Hydrus Microshunt procedures have been studied in randomized, controlled trials. An additional pressure-lowering effect beyond that of cataract surgery was demonstrated only for the latter two procedures (1.9 mmHg and 1.8 mmHg, respectively). Other procedures have only been investigated in cohort studies to date; a pressure-lowering effect was found for some of them. Moreover, iStent and Hydrus Microshunt have been found to slow the progression of visual field defects.

Conclusion: There are robust data documenting the effect of iStent and Hydrus Microshunt in lowering the intraocular pressure and lessening the need for eyedrops. High-quality controlled trials are still needed to test the efficacy of other procedures.

Cite this as:
Voykov B, Prokosch V, Lübke J:
Minimally invasive glaucoma surgery.
Dtsch Arztebl Int 2025; 122: 23–30. DOI: 10.3238/arztebl.m2024.0240

Glaucoma is a group of chronic, progressive, potentially blinding, and irreversible optic neuropathies, whose common feature is a set of morphological changes in the optic disc and retinal nerve fiber layer. These changes are associated with a progressive loss of retinal ganglion cells and a corresponding progressive loss of the visual fields. Because of compensatory mechanisms of the brain, the affected persons only notice the visual field loss when the disease is at an advanced stage (1).

Learning objectives

This article should enable the reader to:

• know the current minimally invasive methods of glaucoma surgery,
• have a realistic idea of the intraocular pressure reduction that can be achieved by these procedures, and
• know the differences between modern minimally invasive methods and the surgical procedures that have long been in established use.

Prevalence

Glaucoma is the leading cause of irreversible blindness worldwide (2). The global prevalence of glaucoma is approximately 3.5% in among persons aged 40 to 80 (3). The prevalence of glaucoma triples with each decade of life (4). It is estimated that the number of persons with glaucoma around the world was more than 64 million people in 2013 and 76 million people in 2020; it is expected to rise to 111 million people in 2040 (3). In 2020, 3.6 million persons worldwide were blind because of glaucoma (5).

In 2006, it was estimated that about 7 in every 100,000 people in Germany were blind or severely visually impaired due to glaucoma, which was the second most common cause of blindness after macular degeneration (6). The Gutenberg Health Study revealed a prevalence of glaucoma of 1.4% among persons aged 35 to 74 (4). A projection yielded a figure of 923,000 people with glaucoma in Germany in 2017 (7). According to the German Federal Statistical Office, 334,600 people who were certified as severely handicapped in 2021 had blindness or visual impairment as their most severe diagnosis. Among these individuals, 66,245 were blind.

The goal of treatment

The goal of glaucoma treatment is to preserve the patients’ visual function (visual acuity and visual fields) and quality of life. The central visual acuity must be maintained, and the risk of losing visual field must be minimized. From an ophthalmological point of view, the only treatment option that has been shown to preserve visual function in glaucoma is to lower the intraocular pressure (2). The extent to which it needs to be lowered depends on a variety of factors including age, initial pressure level, stage of the disease, life expectancy, and the patient’s individual circumstances . The intraocular pressure need not be elevated for glaucoma to develop (statistically normal range 10–21 mmHg), but lowering it is always beneficial in patients with glaucoma (8). In practice, this means that the target intraocular pressure level should be determined individually and adjusted continually over the course of the disease.

Aside from the relative elevation of intraocular pressure, insufficient perfusion of the optic nerves is also thought to play a role in the pathophysiology of glaucoma. Especially in patients whose intraocular pressure is in the statistically normal range, optimizing cardiovascular function is important (9). The mean arterial blood pressure should not fall more than 20% at night compared to the daytime, and it should lie in the range of 65 to 90 mmHg (9). This can only be achieved through interdisciplinary collaboration with specialists from other fields.

The available options for lowering intraocular pressure include eyedrops, laser treatment, and surgery. As a rule, the treatment begins with eyedrops. If the individually determined target pressure level is not reached with eyedrops alone, if the glaucoma findings progress despite treatment, or if drug intolerance develops, the treatment is escalated to laser and surgical procedures.

Conventional filtering surgery can markedly lower the intraocular pressure and achieve long-term control. In these procedures, aqueous humor is drained from the anterior chamber through artificial fistula leading out of the eye and under the conjunctiva. Conventional operations for glaucoma, such as trabeculectomy and glaucoma drainage implants, have been in use for decades (10, 11). Trabeculectomy with the use of cytostatic drugs (mitomycin C and 5-fluorouracil) is still considered the reference standard of glaucoma surgery (10). These procedures, however, may lower the pressure excessively, leading to permanent visual deterioration. The reported frequency of this complication ranges from 3% to 15% (12, 13). The risk of serious bleeding also rises if the intraocular pressure is too low; this occurs in about 1% of patients (13). In the last 10–15 years, many new procedures have been developed to make glaucoma surgery safer. These procedures are much less invasive than the conventional ones and carry a low risk of complications (14). In 2012, Saheb and Ahmed defined this new type of glaucoma surgery as “micro-invasive glaucoma surgery” (MIGS). Ideally, MIGS procedures should meet five criteria: the surgical approach should be ab interno (i.e. starting from the anterior chamber of the eye), the operation should be minimally traumatic and highly biocompatible (without provoking a foreign-body reaction), it should be at least moderately effective and very safe, and the recovery after surgery should be rapid, with minimal impairment of the quality of life until the patient recovers (15).

The definition of MIGS is not entirely uniform, as the European Glaucoma Society (EGS) and the American Glaucoma Society (AGS) offer slightly different definitions. For example, the EGS does not count filtering microstent procedures as MIGS (2). In recent years, many different types of stents, some of them very small, have emerged onto the market, in an attempt to fulfill the promise of minimally invasive surgery. The target group for MIGS procedures consists of those patients who have mild to moderate open-angle glaucoma that can be controlled with one to two eyedrops. As MIGS can easily be combined with cataract surgery, patients who have both cataracts and glaucoma often undergo MIGS as well (16). Compared to conventional filtering procedures such as trabeculectomy or glaucoma drainage implants, MIGS involves a higher target pressure and, as a rule, do not eliminate the need for glaucoma medication after surgery (16). According to the current EGS guidelines, the severity of the glaucoma and the preoperative intraocular pressure should be given particular consideration in the decision-making process (10).

In this CME article, we will present the most important types of MIGS procedures, along with a discussion of the modern variants of conventional filtration surgery (eSupplement). these have also been designated as “minimally-invasive bleb surgery” (MIBS) and are classified by the AGS as a subtype of MIGS called “bleb-forming MIGS”(17).

Types of micro-invasive glaucoma surgery

In what follows, we will present what we consider to be the main types of MIGS and their clinical efficacy. A listing of these techniques is given in Table 1. The anterior chamber of the eye and its various outflow structures are shown schematically in Figure 1.

Figure 1

The anterior chamber of the eye with the structures relevant to the outflow of aqueous humor.

Table 1

Overview and classification of the main current MIGS techniques

Procedures involving the trabecular meshwork

The trabecular meshwork in the angle of the anterior chamber is the first relevant site of outflow resistance for the aqueous humor and thus an obvious surgical target. There are a variety of surgical means of lowering this resistance. The aim of the procedures involving the trabecular meshwork is to open it and clear a path to the canal of Schlemm, which is the next structure in the aqueous humor outflow pathway, thus establishing a connection from the anterior chamber to the canal of Schlemm. This can be achieved either by destroying the trabecular meshwork or by inserting stents.

Destroying the trabecular meshwork

The trabecular meshwork can be opened or removed with a variety of surgical instruments. This can be done either manually with a knife (e.g. the Kahook Dual Blade, Figure 2a) or by electroablation (trabectome). An excimer laser can also be used to create small openings in the trabecular meshwork (excimer laser trabeculotomy, Figure 2b), to enable the outflow of fluid from the chamber into the canal of Schlemm.

Figure 2

Schematic depiction

Stent techniques involving the trabecular meshwork

In addition to destructive methods, there are various stents that can be inserted into the trabecular meshwork. These include the iStent inject W (Figure 2c) and the Hydrus Microshunt (Figure 2d). The iStent is a titanium stent with a length and width of 360 µm that bypasses the trabecular meshwork. The Hydrus Microshunt is an 8-mm-long wire scaffold made of nitinol that additionally widens the canal of Schlemm. Both of these devices can inserted with pre-loaded injectors. According to the manufacturers, both are compatible with MRI of fields strengths up to 3 Tesla.

Pressure reduction by methods involving the trabecular meshwork

In principle, all interventions on the trabecular meshwork can be assumed to yield similar reductions in intraocular pressure by lowering the outflow resistance of the trabecular meshwork. From a physiological point of view, it should make no difference to the aqueous humor flow whether the connection between the anterior chamber and Schlemm’s canal is established by stents or by removal of the meshwork. Many studies of the efficacy of these procedures in reducing the intraocular pressure have dealt with the procedures in combination with cataract surgery. There have been no more than a few controlled trials with carefully selected control groups that have compared the effects of these procedures as a single intervention.

A number of studies have documented the pressure-reducing effect of these procedures when performed in combination with cataract surgery, compared to cataract surgery alone. A Hydrus microshunt in addition to cataract surgery lowered the intraocular pressure to a significantly greater extent than cataract surgery alone (8.3 vs. 6.5 mmHg) and also lowered the consumption of eyedrops of five years of subsequent follow-up a (18). 49.5% of the patients who underwent both procedures achieved an intraocular pressure below 18 mmHg, compared to 33.8% of those who had cataract surgery alone. In contrast, a randomized controlled trial (RCT) comparing the Kahook Dual Blade in addition to cataract surgery with cataract surgery alone showed no additional effect over a follow-up period of one year (19). A Cochrane analysis of the additional effect of stent implantation showed a greater reduction in pressure compared to cataract surgery alone, but overall level of evidence for this conclusion was low (20). This additional effect was, however, also demonstrated in a more recent meta-analysis from 2023: stents were shown both to lower the intraocular pressure and to lessen the use of eyedrops. The intraocular pressure was lowered by 4.7 mmHg by iStent implantation combined with cataract surgery, compared to 2.8 mmHg by cataract surgery alone.

The COMPARE trial showed that the lowering of intraocular pressure is similar for the two stent procedures in combination with cataract surgery, and that the amount of pressure-lowering eyedrops needed after the insertion of a Hydrus Microshunt is significantly lower one year after surgery (22). There have not been any randomized, controlled trials to assess the putative additional benefit of either trabectome or excimer laser trabeculotomy in combination with cataract surgery. For trabectome, however, meta-analyses of observational studies do indeed show a lowering of pressure, even when the procedure is performed alone, i.e., without cataract surgery. The pressure is reportedly lowered by 31% over two years, with the achievement of a target pressure of ca. 15 mmHg (23). Only a few studies have shown a lasting pressure-lowering effect of excimer laser trabeculotomy in combination with cataract surgery: values of ca. 15 mmHg have achieved after up to 8 years of follow-up (24). Nonetheless, the evidence for this procedure, especially as a stand-alone intervention, remains limited.

Procedures involving dilatation of the canal of Schlemm

Ab interno canaloplasty is a method for the dilatation of the canal of Schlemm and the trabecular meshwork. In this procedure (unlike ab externo canaloplasty as described by Stegmann), the canal is opened and dilated from within, but through a minimally invasive approach (16). The goal of canaloplasty is to enhance the physiological outflow of fluid from the chamber through the trabecular meshwork and the canal of Schlemm (25, 26).

Two systems are now available to serve as microcatheters for ab interno canaloplasty:

• the iTrack Advance microcatheter system and
• the OMNI microcatheter.

The two procedures vary slightly in terms of surgical technique.

The safety and efficacy of ab interno canaloplasty (both in isolation and in combination with cataract surgery) have been demonstrated in several studies. In a prospective study, an average reduction in IOP of 32.8% (from 20.4 ± 4.7 mmHg to 13.3 ± 1.9 mmHg) was reported at 12 months after ab interno canaloplasty. Furthermore, the average number of antihypertensive eyedrops was lowered from 2.8 ± 0.9 to 1.1 ± 1.1 , corresponding to an average reduction of 60% (27). Comparable results were reported in further studies (28, 29). All three studies, however, are retrospective case series.

Suprachoroidal techniques

Aside from procedures that bypass the trabecular meshwork or lower its resistance, or widen the canal of Schlemm, another group of minimally invasive procedures create an artificial drainage pathway for the aqueous humor. These include procedures that open up the suprachoroidal space and drain the aqueous humor into it. This space is located between the sclera and the choroid and is anatomically separated from the anterior chamber by the ligament of the ciliary body. Under normal circumstances, this space is closed off from the aqueous humor . The ligament of the ciliary body can, for example, be detached as the result of ocular trauma, thus releasing the suprachoroidal space. As a sharp drop in intraocular pressure can often be observed in such eyes, the idea of using this space for targeted and controlled aqueous drainage has long been entertained. At present, only one implant or procedure is approved in Germany for opening the suprachoroidal space and for aqueous humor drainage there, the so-called MINIject implant. An injector is used to insert the 5-mm-long implant, which is made of sponge-like silicone, into the space to create a connection to the anterior chamber (Figure 2e). A meta-analysis of three prospective, non-randomized studies on the MINIject implant in 66 eyes revealed a lowering of pressure by almost 40% to a mean value of 14.4 mmHg with 1.4 medications applied over two years of follow-up (30). No studies are yet available for a comparison of the MINIject implant with a control group, or concerning its efficacy in combination with cataract surgery.

Studies for the evaluation of the individual procedures are listed in Table 2.

Table 2

Overview of the best available evidence on each of the individual MIGS procedures

Criticism of the MIGS techniques

Although various MIGS procedures have been available for more than a decade, the evidence for most of them is still considered to be weak (10). No clear recommendation can be made for one such procedure over another (10), as only a few high-quality comparative studies between the various MIGS procedures have been performed to date (10). Some of these studies are to be viewed critically because of conflicts of interest, as they were funded by MIGS manufacturers. Others lack information on relevant endpoints, such as complications (31, 32).

Furthermore, many of these studies did not focus on the patient-relevant endpoints of visual acuity and visual field preservation, but instead only used the reduction of intraocular pressure as an endpoint. Data are, exceptionally, available on visual field preservation with iStent and Hydrus implants. For example, a meta-analysis concerning the iStent (which, however, was not limited to randomized, controlled trials) showed that, after iStent implantation, the rate of visual field deterioration was very low (0.024 dB per year) (33). In a randomized controlled trial of the Hydrus microshunt, a deterioration rate of 0.26 dB per year was measured in patients who had undergone combined surgery; this was significantly better than in the group that had undergone cataract surgery alone (34).

The findings of some randomized, controlled trials suggest that MIGS procedures combined with phacoemulsification are superior to phacoemulsification alone. However, long-term results from multiple studies are still lacking, as the follow-up periods are often limited to one to two years, and only selected procedures have been studied in RCTs (10, 35).

Data on complications are scarce; many reports merely state that no clinically relevant complications occurred. However, values for endothelial cell loss are available for the iStent, Hydrus Microshunt, and Miniject implant. The reported values can be considered acceptable for all three procedures (18, 21, 30).

Moreover, aspects such as the experience and training of the glaucoma surgeons and the available infrastructure must be considered as well, especially with newer surgical procedures such as MIGS (10). Some MIGS procedures require higher initial costs, but they are generally easier to learn than conventional glaucoma surgery (10). They are nonetheless demanding techniques that have to be learned (36).

The cost-effectiveness of MIGS procedures is also unclear. A systematic review examined the results of multiple randomized, controlled trials and observational studies, as well as non-randomized controlled trials, comparing MIGS with trabectome or other glaucoma surgery (36). Because the available evidence is limited, no conclusion could be drawn regarding cost-effectiveness, i.e., whether the costs of MIGS are offset by savings over time, resulting from reduced medication or a lesser need for further interventions, among other factors (36).

Discussion

Since the early 2000s, MIGS procedures have been gaining ground as a treatment option for patients with mild to moderate glaucoma [37]. MIGS procedures generally achieve a moderate reduction in intraocular pressure, can lessen the need for pressure-lowering eyedrops, have a favorable safety profile, and can be combined with cataract surgery.

At the same time, the wide range of different procedures with comparable reduction of intraocular pressure and comparable risk profiles also creates a challenge in the choice of the best procedure for each patient (16). The individual target pressure should be the main factor in the choice of procedure. Other factors such as lens status, prior surgery, the condition of the conjunctiva, age, rate of progression, and the stage of glaucoma must be considered as well. There is no consensus yet about the most effective or safest MIGS procedure, and hardly any comparisons between the individual procedures are available.

On the basis of the available literature, the EGS considers trabecular stent procedures to be a suitable treatment for patients with non-progressive, mild to moderate glaucoma in combination with cataract surgery and target pressure in the “mid to upper teens” (10). The aim of trabecular MIGS is generally to lessen the inconvenience and side effects of eyedrops (the “drop burden”) (10). Combining trabecular MIGS with planned cataract surgery appears to be a suitable surgical approach. The time and material resources saved by combined surgery compared to two separate procedures are ecologically and economically beneficial. These procedures can also be performed alone in patients with ocular surface disease, poor adherence, or other comorbidities (10).

Although some authors postulate that the suprachoroidal outflow pathway affords a higher potential of lowering both intraocular pressure and the need for medications than the trabecular outflow pathway (16), the current EGS guideline does not contain any recommendation of this type, because the relevant data are sparse (10). One limitation is the currently low evidence level for most MIGS procedures in terms of reducing intraocular pressure and the need for pressure-reducing medications; in particular, long-term data are lacking (10, 16). The suprachoroidal CyPass microstent can serve as a negative example: it initially showed a very promising 20–30% pressure reduction, with a simultaneous reduction in eyedrop consumption, for up to three years after implantation (38). The COMPASS-XT follow-up study, however, revealed a significant loss of corneal endothelial cells five years after implantation (39), with the result that the CyPass microstent was voluntarily taken off the market. This should be kept in mind when new procedures show good results in studies with relatively short follow-up.

In the future, therefore, randomized and controlled trials with long-term follow-up will be needed so that optimized, evidence-based guidelines can be written for patients with glaucoma.

Acknowledgement

the authors thank Ms. Irena Stingl for creating the figures.

Conflict of interest statement
JL has served as a paid consultant for Santen Pharma and AbbVie and has received lecture honoraria from Alcon, AbbVie, iStar, Glaukos, and Santen Pharma.

VP has received financial support and honoraria for continuing medical education presentations from Alcon, Glaukos, AbbVie, Santen, and Elios.

BV has received personal financial support and honoraria for continuing medical education presentations from AbbVie and Santen.

Manuscript received on 19 August 2024, revised version accepted on 12 November 2024.

Translated from the original German by Ethan Taub, M.D.

Corresponding author
Prof. Dr. med. Jan Lübke

Klinik für Augenheilkunde

Universitätsklinikum Freiburg

Killianstr. 5, 79106 Freiburg, Germany

References

1. Crabb DP, Smith ND, Glen FC, Burton R, Garway-Heath DF: How does glaucoma look?: patient perception of visual field loss. Ophthalmology 2013; 120: 1120–6

2. EGS: European Glaucoma Society Guidelines–5th Edition. 2021.

3. Tham YC, Li X, Wong TY, Quigley HA, Aung T, Cheng CY: Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis. Ophthalmology 2014; 121: 2081–90

4. Höhn R, Nickels S, Schuster AK, et al.: Prevalence of glaucoma in Germany: results from the Gutenberg Health Study. Graefes Arch Clin Exp Ophthalmol 2018; 256: 1695–702

5. GBD 2019 Blindness and Vision Impairment Collaborators, Vision Loss Expert Group of the Global Burden of Disease Study: Causes of blindness and vision impairment in 2020 and trends over 30 years, and prevalence of avoidable blindness in relation to VISION 2020: the Right to Sight: an analysis for the Global Burden of Disease Study. Lancet Glob Health 2021; 9: e144–60.

6. Finger RP, Fimmers R, Holz FG, Scholl HPN: Prevalence and causes of registered blindness in the largest federal state of Germany. Br J Ophthalmol 2011; 95: 1061–7

7. Schuster AK, Wolfram C, Pfeiffer N, Finger RP: [Ophthalmology 2019—where do we stand?: An analysis of the treatment situation in Germany]. Ophthalmologe 2019; 116: 829–37

8. Krieglstein GK: Die „großen Therapiestudien” zum Glaukom. Der Ophthalmologe 2003; 100: 484–92

9. Pillunat KR, Pillunat LE: Vaskuläre Therapiekonzepte bei Glaukompatienten. Ophthalmologe 2021; 118: 431–8

10. Abegao Pinto L, Sunaric Mégevand G, Stalmans I, et al.: European Glaucoma Society—a guide on surgical innovation for glaucoma. Br J Ophthalmol 2023; 107: 1–114

11. Kirwan JF, Lockwood AJ, Shah P, et al.: Trabeculectomy in the 21st century: a multicenter analysis. Ophthalmology 2013; 120: 2532–9

12. Panarelli JF, Moster MR, Garcia-Feijoo J, et al.: Ab-externo microshunt versus trabeculectomy in primary open-angle glaucoma: two-year results from a randomized, multicenter study. Ophthalmology 2024; 131: 266–76

13. Gedde SJ, Herndon LW, Brandt JD, Budenz DL, Feuer WJ, Schiffman JC: Postoperative complications in the tube versus trabeculectomy (TVT) study during five years of follow-up. Am J Ophthalmol 2012; 153: 804–14.e1

14. Chen DZ, Sng CCA: Safety and efficacy of microinvasive glaucoma surgery. J Ophthalmol 2017; 2017: 3182935

15. Saheb H, Ahmed IIK: Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol 2012; 23: 96–104

16. Klabe K, Rüfer F: „Minimally invasive glaucoma surgery“ – Kammerwinkelbasierte Verfahren im Vergleich. Ophthalmologie 2023; 120: 358–71

17. Fellman RL, Mattox C, Singh K, et al.: American glaucoma society position paper: microinvasive glaucoma surgery. Ophthalmol Glaucoma 2020; 3: 1–6

18. Ahmed IIK, Francesco TD, Rhee D, et al.: Long-term outcomes from the HORIZON randomized trial for a schlemm’s canal microstent in combination cataract and glaucoma surgery. Ophthalmology 2022; 129: 742–51

19. Ventura-Abreu N, García-Feijoo J, Pazos M, Biarnés M, Morales-Fernández L, Martínez-de-la-Casa JM: Twelve-month results of ab interno trabeculectomy with kahook dual blade: an interventional, randomized, controlled clinical study. Graefes Arch Clin Exp Ophthalmol 2021; 259: 2771–81

20. Le JT, Bicket AK, Wang L, Li T: Ab interno trabecular bypass surgery with iStent for open-angle glaucoma. Cochrane Database Syst Rev 2019; 3: CD012743

21. Kahale F, Chanbour W, El Zein L, Brenner J, You JY, Melki S: Phacoemulsification with and without iStent: a systematic review and meta-analysis of comparative studies. Ophthalmic Research 2023; 66: 1020–9

22. Ahmed IIK, Fea A, Au L, et al.: A prospective randomized trial comparing hydrus and iStent microinvasive glaucoma surgery implants for standalone treatment of open-angle glaucoma: The COMPARE study. Ophthalmology 2020; 127: 52–61

23. Kaplowitz K, Bussel II, Honkanen R, Schuman JS, Loewen NA: Review and meta-analysis of ab-interno trabeculectomy outcomes. Br J Ophthalmol 2016; 100: 594–600

24. Riesen M, Funk J, Töteberg-Harms M: Long-term treatment success and safety of combined phacoemulsification plus excimer laser trabeculostomy: an 8-year follow-up study. Graefes Arch Clin Exp Ophthalmol 2022; 260: 1611–21

25. Stegmann R, Pienaar A, Miller D: Viscocanalostomy for open-angle glaucoma in black African patients. J Cataract Refract Surg 1999; 25: 316–22

26. Lewis RA, von Wolff K, Tetz M, et al.: Canaloplasty: circumferential viscodilation and tensioning of Schlemm’s canal using a flexible microcatheter for the treatment of open-angle glaucoma in adults: interim clinical study analysis. J Cataract Refract Surg 2007; 33: 1217–26

27. Gallardo MJ, Supnet RA, Ahmed IIK: Viscodilation of schlemm’s canal for the reduction of IOP via an ab-interno approach. Clin Ophthalmol 2018; 12: 2149–55

28. Koerber N, Ondrejka S: Four-year efficacy and safety of iTrack ab-interno canaloplasty as a standalone procedure and combined with cataract surgery in open-angle glaucoma. Klin Monbl Augenheilkd 2023; 240: 1394–404

29. Khaimi MA, Koerber N, Ondrejka S, Gallardo MJ: Consistency in standalone canaloplasty outcomes using the iTrack microcatheter. Clin Ophthalmol 2024; 18: 173–83

30. Dick HB, Mackert MJ, Ahmed IIK, et al.: Two-year performance and safety results of the MINIject supraciliary implant in patients with primary open-angle glaucoma: meta-analysis of the STAR-I, II, III trials. Am J Ophthalmol 2024; 260: 172–81

31. Bonnar J, Azuara-Blanco A: Systematic review of the method and quality of reporting of complications from studies evaluating innovative glaucoma surgical procedures. Eye 2023; 37: 1774–7

32. Rosdahl JA, Gupta D: Prospective studies of minimally invasive glaucoma surgeries: systematic review and quality assessment. Clin Ophthalmol 2020: 14: 231–43

33. Gillmann K, Hornbeak DM: Rates of visual field change and functional progression in glaucoma following trabecular microbypass implantation of iStent technologies: a meta-analysis. BMJ Open Ophthalmol 2024; 9: e001575

34. Montesano G, Ometto G, Ahmed IIK, et al.: Five-year visual field outcomes of the HORIZON trial. Am J Ophthalmol 2023; 251: 143–55

35. Yuan PHS, Dorling M, Shah M, Panarelli JF, Durr GM: Combined micro-invasive glaucoma surgery (MIGS) with phacoemulsification in open angle glaucoma: a systematic review and meta-analysis. Am J Ophthalmol 2024; S0002–9394(24)00333–7.

36. Agrawal P, Bradshaw SE: Systematic literature review of clinical and economic outcomes of micro-invasive glaucoma surgery (MIGS) in primary open-angle glaucoma. Ophthalmol Ther 2018; 7: 49–73

37. Luebke J, Boehringer D, Anton A, Daniel M, Reinhard T, Lang S: Trends in surgical glaucoma treatment in Germany between 2006 and 2018. Clin Epidemiol 2021; 13: 581–92

38. Sandhu A, Jayaram H, Hu K, Bunce C, Gazzard G: Ab interno supraciliary microstent surgery for open-angle glaucoma. Cochrane Database Syst Rev 2021; 5: CD012802

39. Reiss G, Clifford B, Vold S, et al.: Safety and effectiveness of cyPass supraciliary micro-stent in primary open-angle glaucoma: 5-year results from the COMPASS XT study. Am J Ophthalmol 2019; 208: 219–25

40. Sheybani A, Vera V, Grover DS, et al.: Gel stent versus trabeculectomy: the randomized, multicenter, gold-standard pathway study (GPS) of effectiveness and safety at 12 months. Am J Ophthalmol 2023; 252: 306–25

e1. Chen XZ, Liang ZQ, Yang KY, et al.: The outcomes of XEN gel stent implantation: a systematic review and meta-analysis. Front Med (Lausanne) 2022; 9: 804847

e2. Baker ND, Barnebey HS, Moster MR, et al.: Ab-externo microShunt versus trabeculectomy in primary open-angle glaucoma: one-year results from a 2-year randomized, multicenter study. Ophthalmology 2021; 128: 1710–21

e3. Khan A, Khan AU: Comparing the safety and efficacy of preserflo microshunt implantation and trabeculectomy for glaucoma: a systematic review and meta-analysis. Acta Ophthalmol 2024; 102: e443–51